Electron paramagnetic resonance study of electron transfer at the surface of alkaline earth oxides. Reversible pyridine-induced formation of superoxide ions labelled with 17O

Abstract

In the absence of irradiation, it is necessary to use the method of electron transfer between adsorbed species (ETBAS) to stabilise the superoxide ions at the surface of alkaline earth oxides. Identification of the oxygen species as O–2 ions was carried out using 17O-enriched oxygen; results thus obtained were in line with those previously reported for other oxides: two equivalent oxygen nuclei, Axx= 76 G, Ayy and Azz too small to be resolved.

The splitting of the 2pπ* orbitals by the surface crystal field, as measured from the gzz component of the g-tensor depends on the polarizing power q/r of the surface cation acting as the adsorption site. The electron donor sites producing the O–2 molecular ions are the surface, coordinatively unsaturated, O2– ions.